HwB: Mac to C64 Nullmodem Cable

Mac to C64 Nullmodem Cable

The RS-232 standard on the C64 is a little bit strange. It
uses inverted TTL level for the signals. The RS-422 ports on the
Macintosh has both an inverted and non-inverted input. By using
the inverted instead of non-inverted the inverted C64 level is
back to normal.